From the past, acoustic devices that replay audio contents, and that output replayed audio from speakers, have often been mounted to moving bodies such as vehicles and so on. Due to this, it has been possible for users to enjoy replayed audio contents even in the spaces within the bodies of the moving bodies.
Now, a moving body is generally provided with an engine or the like that generates drive power. The operating sound of such an engine or the like constitutes extraneous noise from the point of view of listening to the reproduction of audio contents in the space within the moving body, and in particular it is often the case that the operating noise of such an engine is very loud.
Due to this, techniques of various sorts have been proposed as methods for controlling noise in the space within a moving body. One such technique is a technique of determining whether or not to perform control operation for active noise cancellation, according to the level of influence of the noise upon the audio sound (i.e. upon the sound of the contents being replayed) on the basis of a noise level that is obtained based upon the result of sound pickup within the vehicle passenger compartment (refer to Patent Document #1: hereinafter termed the “prior art example”).